Offset calibration system and method of automatic power control loop

ABSTRACT

An offset calibration system of a control loop at least comprises a pre-amplifier circuit and a post-amplifier circuit. The pre-amplifier circuit generates a pre-output signal and then transmits the pre-output signal to the post-amplifier circuit to amplify. The offset calibration system comprises a comparator, an offset calibration module, and a determination circuit. The comparator compares the pre-output signal with a predetermined pre-reference signal to generate a pre-compared signal. The offset calibration module stores a predetermined and adjustable offset calibration value for adding to the pre-output signal. The determination circuit adjusts the offset calibration value based on the pre-compared signal, so the offset calibration value can be added to the pre-output signal dynamically to compensate and calibrate the offset of the pre-output signal caused by the pre-amplifier circuit to avoid the post-amplifier circuit amplifying the offset of the pre-output signal again.

FIELD OF THE INVENTION

The present invention relates to an offset calibration system and methodof an automatic power control loop for calibrating the offset generatedby the automatic power control loop.

BACKGROUND OF THE INVENTION

When the pickup head of an optical information recording/readingapparatus writes and reads pits of a compact disk, an automatic powercontrol loop is used to control and adjust the laser power of the laserdiode within the pickup head. A pickup head comprises a laser diode, alaser diode driver and a laser power detector. The laser diode providesa laser source to read or write data on the compact disk. The laserpower detector detects the laser power of the laser beam to output acorresponding laser power detection signal.

The pickup head uses different laser powers when it is writing orreading. The power in writing is higher than the power in reading. It isimportant to control the power of the laser emitted by the laser diode.The laser diode is driven by the laser diode driver. Hence, controllingthe laser diode driver can further control the laser power.

The automatic power control loop controls the laser diode driver tooutput an electric current to drive the laser diode for emitting a laserbean with an adequate laser power. The laser power detection signaloutputted by the laser power detector and the laser power of thedetected laser beam are in inverse proportion. The laser power detectionsignal will be sampled and held by a sample/hold circuit of theautomatic power control loop, and then transmitted to a pre-amplifierfor amplifying and generating a pre-output signal. The pre-output signalis subtracted by a predetermined reference signal in an adder. If theresult value does not equal to zero, the laser power of the laser beamstill needs to be adjusted. A post-amplifier can adjust the pre-outputsignal and generate a power control signal. The post-amplifier transmitsthe power control signal to the laser diode driver for emitting anadequate laser power. In an ideal condition, when the laser diodedoesn't emit the laser beam, the pre-output signal is the predeterminedreference signal.

In general, the prior art control and calibration method for the laserpower emitted by the laser diode can adjust the laser power very well.However, in the prior art, when the laser power detector generates thelaser power detection signal with an offset, the automatic power controlloop can't calibrate immediately. Through the amplifier, the offset isamplified and may be beyond the range that the adder can adjust.Therefore, a wrong power control signal is produced resulting in a wronglaser power. Consequently, mistakes occur in writing/reading data of thecompact.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present invention to providean offset calibration system and method of an automatic power controlloop for calibrating a laser power emitted from a laser diode so thatthe laser diode can emit accurate laser power.

The automatic power control loop of the present invention comprises apre-amplifier circuit and a post-amplifier circuit. The pre-amplifiercircuit generates a pre-output signal and then transmits the pre-outputsignal to the post-amplifier circuit for amplifying. The offsetcalibration system comprises a comparator, an offset calibration moduleand a determination circuit. The comparator compares the pre-outputsignal with a predetermined pre-reference signal to generate apre-compared signal. The offset calibration module stores apredetermined and adjustable offset calibration value for adding to thepre-output signal. The determination circuit electrically connects tothe comparator and the offset calibration module to adjust the offsetcalibration value stored in the offset calibration module based on thepre-compared signal generated by the comparator.

The determination circuit adjusts the offset calibration valuedynamically based on the pre-compared signal, so the offset calibrationvalue can be added to the pre-output signal dynamically to compensateand calibrate the offset of the pre-output signal caused by thepre-amplifier circuit. That will avoid the post-amplifier circuitamplifies the offset of the pre-output signal again.

The present invention calibrates the offset of an automatic powercontrol loop by the offset calibration system. The offset of thepre-output signal can be compensated and calibrated immediately by theoffset calibration system of the present invention to avoid that thepost-amplifier circuit amplifies the offset of the pre-output signalagain.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after the followingdetailed description of the preferred embodiment, which is illustratedin the various figures and drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 is the block diagram according to the offset calibration systemof the automatic power control system in the present invention.

FIG. 2 is the block diagram of the pre-amplifier circuit and thepost-amplifier circuit according to FIG. 1.

FIG. 3 is the flow chart of the automatic power control loop and theoffset calibration system of the present invention according to FIG. 1and FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Please refer to FIG. 1. FIG. 1 is a block diagram of an offsetcalibration system 20 of an automatic power control system 1 accordingto the present invention. The present invention is an offset calibrationsystem 20 of a control loop 1. The control loop 1 comprises apre-amplifier circuit 10 and a post-amplifier circuit 11. Thepre-amplifier circuit 10 generates a pre-output signal S1 and thentransmits the pre-output signal S1 to the post-amplifier circuit 11 toamplify. The control loop 1 is an automatic power control loop tocontrol a laser source device 30.

The laser source device 30 comprises a laser diode 32 and a laser diodedriver 31. The automatic power control loop 1 controls the laser diodedriver 31 to output a driving electric current to drive a compact disksystem (not show in FIG. 1) with the laser beam when the compact disksystem reads or writes a compact disk. The compact disk system comprisesa pickup head which comprises a laser power detector to detect a laserpower of the laser beam, and to ouput a corresponding laser powerdetection signal. The laser power detection signal and the detectedlaser power of the laser beam are in inverse proportion.

The offset calibration system 20 of the present invention comprises acomparator 22, an offset calibration module 24, a determination circuit26, and a pre-adder 28. A comparator 22 compares the pre-output signalS1 with a predetermined pre-reference signal Sref to generate apre-compared signal S2. The offset calibration module 24 stores apredetermined and adjustable analog offset calibration value AOC foradding to the pre-output signal S1. The determination circuit 26electrically connects to the comparator 22 and the offset calibrationmodule 24 to adjust the analog offset calibration value AOC stored inthe offset calibration module 24 based on the pre-compared signal S2generated by the comparator 22. The pre-adder 28 makes the analog offsetcalibration value AOC add to the pre-output signal S1 to become acalibrated pre-output signal SC, and then transmits the calibratedpre-output signal SC to the post-amplifier circuit 11.

The determination circuit 26 adjusts the analog offset calibration valueAOC dynamically based on the pre-compared signal S2, so the analogoffset calibration value AOC can be added to the pre-output signal S1dynamically to compensate and calibrate the offset of the pre-outputsignal S1 caused by the pre-amplifier circuit 10 to avoid that thepost-amplifier circuit 11 amplifies the offset of the pre-output signalS1 again.

The offset calibration module 24 comprises a pre-register 241 and apre-D/A converter 242. The pre-register 241 stores a digital offsetcalibration value DOC. The pre-D/A converter 242 converts the digitaloffset calibration value DOC to a corresponding analog offsetcalibration value AOC. The analog offset calibration value AOC will besent to the pre-adder 28, and then added to the pre-output signal S1.

In an ideal situation, when the laser diode 32 doesn't emit the laserbeam, the pre-output signal S1 generated by the pre-amplifier circuit 10is the predetermined pre-reference signal Sref. Only when the laserdiode 32 doesn't emit the laser beam, the determination circuit 26 willadjust the offset calibration value based on the pre-compared signal S2to make the pre-adder 28 add the analog offset calibration value AOC tothe pre-output signal S1 for compensating and calibrating.

Please refer to FIG. 2. FIG. 2 is a block diagram of the pre-amplifiercircuit 10 and the post-amplifier circuit 11 shown in FIG. 1. Thepre-amplifier 10 comprises a sample/hold circuit 12 and a pre-amplifier14. The sample/hold circuit 12 samples and holds the laser powerdetection signal according to a control signal, and outputs asample/hold signal S/h. The pre-amplifier 14 receives and amplifies thesample/hold signal S/h outputted from the sample/hold circuit 12 togenerate the pre-output signal S1. The pre-output signal S1 then isinputted to the offset calibration system 20 of the present inventionfor calibrating the offset.

As shown in FIG. 2, the calibrated pre-output signal SC is inputted tothe post-amplifier circuit 11. The post-amplifier circuit 11 provides apower control signal SP to control a laser diode driver 31 of the lasersource device 30. The post-amplifier circuit 11 comprises apost-register 13, a post-D/A converter 15, a post-subtractor 17, and apost-amplifier 19. The post-register 13 stores a digital poweradjustment value. The post-register 13 comprises a plurality of storageunits to store the digital power adjustment value, and the number ofstorage units in the post-register 13 determines the range of thedigital power adjustment value. The determination circuit 26 in FIG. 1adjusts the offset calibration value according to the pre-comparedsignal S2 to make the analog offset calibration value AOC added to thepre-output signal S1 to avoid the pre-output signal S1 being beyond therange of the power adjustment value in the post-register 13.

The post-D/A converter 15 converts the digital power adjustment value toa corresponding analog power adjustment value. The post-subtractor 17adds the analog power adjustment value to the calibrated pre-outputsignal SC to become a post-output signal S3. The post-amplifier 19receives and amplifies the signal from the post-subtractor 17 togenerate the power control signal SP. The power control signal SP cancontrol the laser diode driver 31, and further control the laser powerof the laser beam emitted from the laser diode 32.

Please refer to FIG. 3. FIG. 3 is a flow chart of the automatic powercontrol loop 1 and the offset calibration system 20 of the presentinvention according to FIG. 1 and FIG. 2. The method comprises thefollowing steps:

Step S31: sampling and holding a laser power detection signal accordingto a control signal, and outputting a sample/hold signal S/h;

Step S32: amplifying the sample/hold signal S/h to generate a pre-outputsignal S1;

Step S33: storing a digital offset calibration value DOC;

Step S34: comparing the pre-output signal S1 with a predeterminedreference signal Sref to generate a pre-compared signal S2;

Step S35: dynamically adjusting the digital offset calibration value DOCaccording to the pre-compared signal S2;

Step S36: converting the digital offset calibration value DOC to acorresponding analog offset calibration value AOC;

Step S37: dynamically adding the analog offset calibration value AOC tothe pre-output signal S1 to become the calibrated pre-output signal SCto compensate and calibrate the offset of the pre-output signal causedby the pre-amplifier circuit to avoid the post-amplifier circuitamplifying the offset of the pre-output signal again;

Step S38: storing a power adjustment value in a digital way;

Step S39: converting the digital power adjustment value to acorresponding analog power adjustment value;

Step S40: adding the analog power adjustment value to the calibratedpre-output signal SC to become a post-output signal S3;

Step S41: receiving and amplifying the post-output signal S3 to generatea power control signal SP.

The present invention utilizes an offset calibration system to compareand calibrate the pre-output signal generated by the pre-amplifiercircuit. The invention makes the offset of the pre-output signalcalibrated by the offset calibration system before outputted into thepost-amplifier circuit to avoid the pre-output signal with offset to betransmitted to the post-amplifier circuit, so to avoid the offset beingbeyond the range of the power adjustment value. After amplifying, theoffset will become the larger power control signal. However, the offsetof the pre-output signal has been calibrated by the offset calibrationsystem of the present invention, so that mistakes will not occur whenwriting/reading data of the compact disk system. This appears theadvantage and the utility of the offset calibration system in thepresent invention.

The description of the above-mentioned preferred embodiments provides abetter understanding on the strengths and spirits of this presentinvention, not to limit the domain of the invention. Moreover, it aimsto include various modification and arrangement parallel in form intothe domain of the patent applied by this present invention. Due to theabove mention, the domain of the patent applied by the invention shouldbe explained in a macro view to cover all kinds of possible modificationand arrangement of equal form.

What is claimed is:
 1. An offset calibration system of an automaticpower control loop which at least comprises a pre-amplifier circuit anda post-amplifier circuit, said pre-amplifier circuit generating apre-output signal and then transmitting said pre-output signal to thepost-amplifier circuit to amplify, said offset calibration systemcomprising: a comparator for comparing said pre-output signal with apredetermined pre-reference signal to generate a pre-compared signal; anoffset calibration module for storing a predetermined and adjustableoffset calibration value; a determination circuit for electricallyconnecting to said comparator and said offset calibration module, andadjusting said offset calibration value stored in said offsetcalibration module based on said pre-compared signal generated by saidcomparator; and a pre-adder for making said offset calibration valueadded to said pre-output signal; wherein said determination circuitadjusts said offset calibration value dynamically based on saidpre-compared signal, so said offset calibration value can be added tothe pre-output signal dynamically to compensate and calibrate the offsetof said pre-output signal caused by said pre-amplifier circuit to avoidsaid post-amplifier circuit amplifying the offset of said pre-outputsignal again, wherein said automatic power control loop is used forcontrolling a laser source device which comprises a laser diode and alaser diode driver, and said automatic power control loop controls saidlaser diode driver to output a driving electric current to drive saidlaser diode which emits a corresponding laser beam.
 2. The offsetcalibration system according to claim 1, wherein said laser diodeprovides a compact disk system with said laser beam when said compactdisk system reads or writes a compact disk, said compact disk systemcomprising a pickup head which comprises a laser power detector todetect a laser power of said laser beam reflecting from said compactdisk, and output a corresponding laser power detection signal.
 3. Theoffset calibration system according to claim 2, wherein saidpre-amplifier circuit comprises: a sample/hold circuit for sampling andholding said laser power detection signal according to a control signal;and a pre-amplifier for receiving and amplifying the signal outputtedfrom said sample/hold circuit to generate said pre-output signal.
 4. Theoffset calibration system according to claim 2, wherein said laser powerdetection signal outputted from said laser power detector and saiddetected laser power of said laser beam are in inverse proportion. 5.The offset calibration system according to claim 1, wherein in an idealcondition, when said laser diode doesn't emit said laser beam, saidpre-output signal generated by said pre-amplifier circuit is saidpredetermined pre-reference signal.
 6. The offset calibration systemaccording to claim 5, wherein when said laser diode doesn't emit saidlaser beam, said determination circuit will adjust said offsetcalibration value based on said pre-compared signal to make said offsetcalibration value added to said pre-output signal for compensating andcalibrating.
 7. The offset calibration system according to claim 1,wherein said offset calibration module comprises: a pre-register forstoring said offset calibration value digitally; and a pre-D/A converterfor converting said digital offset calibration value to a correspondinganalog offset calibration value to be sent to said pre-adder.
 8. Theoffset calibration system according to claim 1, wherein saidpost-amplifier circuit, which provides a power control signal to controlsaid laser diode driver, comprises: a post-register for storing adigital power adjustment value; a post-D/A converter for converting saiddigital power adjustment value to a corresponding analog poweradjustment value; a post-subtractor for adding said analog poweradjustment value to said pre-output signal; and a post-amplifier forreceiving and amplifying the signal from said post-subtractor togenerate said power control signal.
 9. The offset calibration systemaccording to claim 8, wherein said post-register comprises a pluralityof storage units to store said digital power adjustment value, and thenumber of storage units in said post-register determines the range ofsaid digital power adjustment value.
 10. An offset calibration method ofan automatic power control loop which at least comprises a pre-amplifiercircuit and a post-amplifier circuit, said pre-amplifier circuitgenerating a pre-output signal and then transmitting said pre-outputsignal to the post-amplifier circuit to amplify, said offset calibrationmethod comprising; comparing said pre-output signal with a predeterminedpre-reference signal to generate a pre-compared signal; dynamicallyadjusting a pre-stored offset calibration value according to saidpre-compared signal; and dynamically adding said offset calibrationvalue to said pre-output signal to compensate and calibrate the offsetof said pre-output signal caused by said pre-amplifier circuit to avoidsaid post-amplifier circuit amplifying the offset of said pre-outputsignal again, wherein said automatic power control loop is used forcontrolling a laser source device which comprises a laser diode and alaser diode driver, and said automatic power control boo controls saidlaser diode driver to output a driving electric current to drive saidlaser diode which emits a corresponding laser beam.
 11. The offsetcalibration method according to claim 10, wherein said laser diodeprovides a compact disk system with said laser beam when said compactdisk system reads and writes a compact disk, said compact disk systemcomprising a pickup head which comprises a laser power detector todetect a laser power of said laser beam reflecting from said compactdisk, and output a corresponding laser power detection signal.
 12. Theoffset calibration method according to claim 11, wherein said methodfurther comprises: sampling and holding said laser power detectionsignal according to a control signal; and amplifying said detectionsignal outputted from said sample/hold circuit to generate saidpre-output signal.
 13. The offset calibration method according to claim11, wherein said laser power detection signal outputted from said laserpower detector and said detected laser power of said laser beam are ininverse proportion.
 14. The offset calibration method according to claim10, wherein in an ideal condition, when said laser diode doesn't emitsaid laser beam, said pre-output signal generated by said pre-amplifiercircuit is said predetermined pre-reference signal.
 15. The offsetcalibration method according to claim 14, wherein when said laser diodedoesn't emit said laser beam, said offset calibration value is adjustedbased on said pre-compared signal to make said offset calibration valueadded to said pre-output signal for compensating and calibrating. 16.The offset calibration method according to claim 10, wherein said offsetcalibration method further comprises: storing said offset calibrationvalue digitally; and converting said digital offset calibration value toa corresponding analog offset calibration value to be added to saidpre-output signal.
 17. The offset calibration method according to claim10, wherein said post-amplifier circuit provides a power control signalto control said laser diode driver by the following steps: storing adigital power adjustment value; converting said digital power adjustmentvalue to a corresponding analog power adjustment value; adding saidanalog power adjustment value to said pre-output signal; and receivingand amplifying said pre-output signal to said analog power adjustmentvalue to generate said power control signal.
 18. The offset calibrationmethod according to claim 17, wherein said post-amplifier circuitcomprises a post-register which has a plurality of storage units tostore said digital power adjustment value, and the number of saidstorage units in said post-register determines the range of said digitalpower adjustment value.